PROJECT SUMMARY Alzheimer's disease (AD) is the most common cause of dementia. Underlying pathological and physiological changes related to the onset and progression of AD are believed to emerge several years prior to clinical manifestations. Sensory impairments, gait abnormalities, and motor slowing may precede the diagnosis of AD by a decade or more, presenting the exciting possibility that changes in sensorimotor functioning may act as early noninvasive biomarkers for AD. Previous work by our group has identified links between cognitive performance and sensory impairment and gait speed and variability, making them potential preclinical markers of early AD pathology. We propose to use up to 10 years of existing longitudinal data, and ongoing/new data collection in approximately 1,000 older adults in the Baltimore Longitudinal Study of Aging (BLSA), to examine the roles of sensory function, gait speed and variability, and free-living measures of daily physical activity (PA) as precursors to cognitive impairment. We will also determine the link between sensorimotor measures and biomarkers of AD pathology, including A? deposition using [11C]-Pittsburgh compound B positron emission tomography, brain atrophy using structural magnetic resonance imaging (MRI), Tau and pTau from cerebrospinal fluid, and cognitive performance. We will further utilize the rich data resources of the BLSA to develop a parsimonius prediction model for risk of progression to MCI/AD, and validate its performance in the Atherosclerosis Risk in Communities (ARIC) study. A better understanding of the associations among sensorimotor changes, subclinical AD pathology, and cognitive performance may elucidate a high-risk phenotype that is associated with increased risk of poor cognitive outcomes over time and increase our understanding of the complex associations among declines in sensory, physical, and cognitive functioning with age. To this end, future intervention studies of AD prevention might screen for sensorimotor impairments as a high-risk phenotype reflective of increased risk for developing AD, which could serve as surrogate outcomes in clinical trials. Moreover, sensorimotor impairments may present feasible and modifiable targets for AD prevention by identifying critical threshold(s) for implementation of assistive and rehabilitative technologies such as hearing aids, corrective lenses, surgical or pharmacologic procedures to correct hearing and/or vision impairment (e.g., cataract surgery, cochlear implants), and physical therapy/timing and coordination of movement training to correct gait abnormalities.